Cooling device with controllable evaporation temperature

ABSTRACT

A cooling device for cooling a test sample has at least two cascade cooling stages, each with at least one coolant line, one compressor ( 1.1, 2.1 ), one relief throttle ( 1.4, 2.4 ), one evaporator ( 6, 7 ) and one liquefier ( 3, 6 ). The cooling device has an additional relief throttle disposed between the evaporator ( 7 ) of the last cascade cooling stage and the compressor ( 2.1 ) of the last cascade cooling stage. This represents a simple possibility of adjusting the cooling temperature, thereby avoiding the use of valves that can be adjusted at low temperatures, since these are complex and expensive.

This application claims Paris Convention priority of DE 10 2011 006 165.7 filed Mar. 25, 2011 the complete disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention concerns a cooling device for cooling a test sample, comprising at least two cascade cooling stages, each comprising at least one coolant line, one compressor, one relief throttle, one evaporator and one liquefier.

Devices having such properties are e.g. the device NMR90 of the company Millrock Technology, Kingston, N.Y., USA, the device ULSP90 of the company ULSP by, Ede, NL and the device FTS XR Air Jet of the company RototecSpintec GmbH, Biebesheim, Germany.

Various analysis methods require cooling of the samples to be analyzed. In specific cases, such as nuclear magnetic resonance spectroscopy or X-ray crystallography, this is often achieved by introducing the sample into a cold gas flow (cooling gas), advantageously nitrogen or helium.

This cold gas flow may be realized e.g. through evaporation of liquid gases or cooling a warm gas using heat exchangers that are immersed into liquefied gas. Provision or generation and storage of these liquefied gases requires complex logistics.

The warm gas may alternatively also be cooled using a coolant cycle process. In a cycle process, a suitable coolant is compressed in a compressor to a higher pressure and is thereby heated, then cooled (desuperheated) in a heat exchanger to a temperature below the liquefaction temperature that prevails at the obtained pressure, thereby dissipating heat, is further liquefied, thereby dissipating further heat, is relieved by a suitable throttle to a lower pressure, and evaporated again in a second heat exchanger, thereby absorbing heat from the gas to be cooled at the low evaporation temperature.

There are conventional configurations of coolant cycle processes with adjustable evaporation pressure and adjustable throttle between the first heat exchanger (coolant liquefier) and second heat exchanger (coolant evaporator) in order to adjust the desired cooling temperature. Such a configuration is technically complex when the cycle process to be varied is already operated in a cascade of cycle processes at a very low liquefaction temperature and the adjustable throttle consequently also becomes very cold.

For this reason, it is current practice to largely do without adjustment of the desired coolant temperature. This applies to the devices of the companies Bruker (type “BCU-X”), ULSP type “90 Immersion Probe Cooler”, and Milrock type “NMR90 sample cooler”. In an alternative fashion, the gas flow that has been cooled to a predetermined temperature is heated to a desired higher temperature by means of an installed heating device. One example therefore are the devices of the company RototecSpintec FTS “XR Air-Jet Cooler”.

It is the underlying purpose of the present invention to provide a simple way of adjusting the cooling temperature, thereby avoiding the use of valves that can be adjusted at low temperatures, since these are complex and expensive.

SUMMARY OF THE INVENTION

This object is achieved in a surprisingly simple and yet effective fashion in that an additional relief throttle is arranged between the evaporator of the last cascade cooling stage and the compressor of the last cascade cooling stage.

In the inventive cooling device, the evaporated coolant is relieved once more downstream of the second heat exchanger (evaporator). For this reason, the overall decompression between the high-pressure and low-pressure side of the evaporator is divided into two partial decompressions, wherein the pressure that is generated inbetween in the evaporator is influenced by the adjustable throttle of the second partial decompression. The coolant is evaporated in the second heat exchanger, which is disposed between the two throttles, thereby providing the desired cooling power at the evaporation temperature of the coolant at this adjustable pressure, and for this reason, the cooling temperature can also be influenced.

In contrast to the methods that are normally used, the throttle does not need to be adjustable itself, which could be realized only with great technical expense in a cascade of cycle processes of a cycle process to be varied with a very low liquefying temperature and therefore low throttle temperature.

One further advantage of this invention results from the fact that, when a higher temperature and therefore higher evaporation pressure in the second heat exchanger is desired, the suction pressure in the compressor is lower due to the necessary increased decompression at the second throttle, which decreases the power input of the compressor. In contrast thereto, a throttle which is adjusted at a low temperature between the first and the second heat exchanger would entail a higher suction pressure and therefore higher power input of the compressor when adjusting a higher evaporation temperature with consequently reduced cooling power requirements.

One particularly advantageous embodiment is characterized in that the additional relief throttle is designed in two stages in the form of a parallel arrangement of a bypass valve and an invariable relief throttle. This provides a variable relief throttle with simple and inexpensive means.

In an alternative variant, the additional relief throttle is designed in the form of a variable adjustable relief throttle.

One further advantageous embodiment is characterized in that the evaporator of the last cascade cooling stage is designed as a heat exchanger, a cooling gas enters the heat exchanger through a gas inlet, dissipates heat and exits the heat exchanger again through a gas outlet, and the cooled cooling gas is guided to the test sample for cooling it. With this design, the heat exchanger is simultaneously the transfer line for the cooling gas and the device can be designed in a simple and space-saving fashion.

The invention is particularly advantageous when the cooling device is part of a nuclear magnetic resonance spectroscopy apparatus, in which the cooled gas flow is heated to the desired temperature and higher temperatures can be achieved with less cooling and therefore also less heating, which simplifies control.

The inventive cooling device may alternatively also be part of an X-ray spectroscopy apparatus. In particular, X-ray crystallography often requires cooling of the test samples.

The inventive cooling device is alternatively also advantageously part of an EPR apparatus.

Further advantages of the invention can be extracted from the description and the drawing. The features mentioned above and below may be used individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic view of an embodiment of the inventive cooling device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The cooling device shown by way of example in FIG. 1 includes a first cascade cooling stage with compressor 1.1, safety pressure switch 1.2, filter 1.3, relief throttle 1.4, and pressure compensating vessel 1.5 as well as a second cascade cooling stage with compressor 2.1, safety pressure switch 2.2, filter 2.3, relief throttle 2.4, and pressure compensating vessel 2.5.

A combined air heat exchanger with fan 5 is e.g. used as liquefier 3 for the first cascade cooling stage and as desuperheater 4 for the second cascade cooling stage.

A heat exchanger 6 is used as evaporator for the first cascade cooling stage and as liquefier for the second cascade cooling stage.

An evaporator (heat exchanger) 7, illustrated by way of example as transfer line of the cooling gas, is used as evaporator for the second cascade cooling stage to provide the desired cooling power in that the gas to be cooled is guided from the inlet 7.1 to the outlet 7.2.

In accordance with the invention, the desired temperature is adjusted by changing the evaporation pressure of the coolant in the second stage of a cooling cascade, illustrated herein by way of example, via a variable throttle on the return path of the coolant from the evaporator 7 to the entry into the compressor 2.1. This variable throttle is illustrated in FIG. 1 by way of example by an invariable relief throttle 2.6 and a bypass valve 2.7 for bypassing this throttle. This results in a lower relief pressure when the bypass valve 2.7 is open and in a higher relief pressure in the evaporator 7 when the bypass valve is closed, and therefore in a lower or higher evaporation temperature. Instead of the invariable relief throttle 2.6 and the bypass valve 2.7, it is also possible as an alternative for the illustrated example to use a variable throttle in the form of an adjustable needle valve.

Although the invention is illustrated above by means of a cooling device in accordance with the principle of a compression cooling machine with two-stage cooling cascade, adjustment of the evaporation temperature by means of a variable throttle between the coolant evaporator and the compressor inlet is also possible with one-stage cooling devices according to this principle as well as with cooling cascades with more than two stages.

LIST OF REFERENCE NUMERALS

1.1 compressor of the first cascade cooling stage

1.2 safety pressure switch thereof

1.3 filter thereof

1.4 relief throttle thereof

1.5 compensating vessel thereof

2.1 compressor of the second cascade cooling stage

2.2 safety pressure switch thereof

2.3 filter thereof

2.4 relief throttle thereof

2.5 compensating vessel thereof

2.6 relief throttle for adjusting a higher evaporation pressure of the second cascade cooling stage

2.7 bypass valve for bypassing the relief throttle 2.6 for adjusting a lower evaporation pressure of the second cascade cooling stage

3 liquefier of the first cascade cooling stage

4 desuperheater of the second cascade cooling stage

5 fan for liquefier 3 and desuperheater 4

6 heat exchanger as evaporator of the first cascade cooling stage and liquefier of the second cascade cooling stage

7 heat exchanger as evaporator of the second cascade cooling stage for providing the cooling power by cooling a gas

7.1 entry of the gas to be cooled

7.2 exit of the cooled gas 

1. A cooling device for cooling a test sample, the cooling device comprising: at least one first cascade non-final cooling stage, said first non-final cooling stage having at least one first coolant line, a first compressor, a first relief throttle, a first evaporator and a first liquefier; and a second final cascade cooling stage, said second final cascade cooling stage having at least one second coolant line, a second compressor, a second relief throttle, a second evaporator, a second liquefier and an additional relief throttle disposed between said second evaporator and said second compressor.
 2. The cooling device of claim 1, wherein said additional relief throttle is designed in two stages as a parallel arrangement of a bypass valve and an invariable relief throttle.
 3. The cooling device of claim 1, wherein said additional relief throttle is designed as a variable adjustable relief throttle.
 4. The cooling device of claim 1, wherein said second evaporator is designed as a heat exchanger, wherein a cooling gas enters said heat exchanger through a gas inlet, dissipates heat, exits said heat exchanger again through a gas outlet and is guided to the test sample for cooling thereof.
 5. The cooling device of claim 1, wherein the cooling device is structured for use in a nuclear magnetic resonance spectroscopy apparatus.
 6. The cooling device of claim 1, wherein the cooling device is structured for use in an X-ray spectroscopy apparatus.
 7. The cooling device of claim 1, wherein the cooling device is structured for use in an EPR apparatus. 